Are you looking for larger pieces, smaller pieces? I am cleaning my tank today and I have rock all over in my sump. I wouldn't mind getting rid of some of it. I can stick some in a bucket today if you would like.
i also have a bunch of rock that may work for you, about a 5 gallon bucket full or so. it needs cleaned up but i can work on it this week if it's what you're looking for. size preference?